Hydrogen peroxide is widely used to clean and disinfect contact lenses, normally generated in situ from effervescing tablets containing sodium percarbonate and citric acid. Hydrogen perioxide is effective for this purpose but any excess hydrogen peroxide can cause ocular irritation when the contact lens is re-inserted into the eye. To remove such excess hydrogen peroxide, repeated washings and rinsings of the lens are necessary but this is unacceptable in the case of soft contact lenses since undesirable leaching of isotonic solutions from the lenses can occur. An alternative procedure that has been suggested is to neutralize the hydrogen peroxide by chemical means e.g. by treating the solution with slowly released sodium nitrite or sodium sulphite. such a method however has the disadvantage of leaving the neutralizing chemicals in the lens-treating solution which may themselves cause ocular irritation.
European Published Patent Application No. 0082798A discloses a regime for the treatment of contact lenses by disinfecting and cleaning them with a hydrogen peroxide solution and then treating with catalase, firstly by adding catalase to the hydrogen peroxide solution, secondly by pouring off the hydrogen peroxide solution and adding a catalase solution or by transferring the lenses to another vessel containing a catalase solution.
The methods disclosed in that European published patent application possess the severe disadvantage that the use of catalase as a solution requires the solution to be preserved; this means that extraneous preservative is in contact with the lenses and may therefore require its own removal regime before the lenses may be safely inserted into the eyes of a wearer.
According to a first aspect of the present invention there is provided a method of treating a contact lens by means of hydrogen peroxide, which method comprises conducting the hydrogen peroxide treatment of the lens in the presence of an immobilized enzyme which catalyses the decomposition of hydrogen peroxide.
According to a second aspect of the present invention there is provided a method of decomposing hydrogen peroxide used for treating a contact lens which method comprises contacting the hydrogen peroxide with an immobilized enzyme which catalyzes the decomposition of hydrogen peroxide.
According to a further aspect of the present invention there is provided apparatus for treating contact lenses with hydrogen peroxide which apparatus includes an effective amount of an immobilized enzyme capable of catalyzing the decomposition of hydrogen peroxide. The apparatus may comprise a container bearing a suitable quantity of a said immobilized enzyme.